The present invention is directed to intercalated layered materials and, optionally, exfoliates thereof, prepared by intercalating a layered material, e.g., a phyllosilicate, such as a smectite clay, with a polyolefin intercalant, preferably polyethylene and/or polypropylene, and a maleic anhydride-modified polyolefin intercalant. The intercalated layered material, preferably in the form of a concentrate, is combined with a polyolefin matrix polymer since the addition of a polyolefin matrix polymer, after shearing the concentrate for exfoliation, avoids degradation of the polyolefin matrix polymer, added after shearing of the concentrate. The polyolefin and a maleic anhydride-modified polyolefin polymer can be intercalated in the form of a polymer or an oligomer capable of polymerization to form the polymer, (e.g., an ethylene oligomer or polymer and/or a propylene oligomer or polymer and/or copolymers thereof) or, can be unexpectedly easily intercalated as the oligomer or polymer by direct compounding, e.g., by combining the polyolefin oligomer and/or polymer in a mixing or extruding device at or above the polyolefin polymer melt temperature, to produce the intercalated layered material and, subsequently, the nanocomposite by addition of matrix polyolefin polymer.
It is well known that phyllosilicates, such as smectite clays, e.g., sodium montmorillonite, sodium bentonite, calcium bentonite, and calcium montmorillonite, can be treated with organic molecules, such as organic ammonium ions, to intercalate the organic molecules between adjacent, planar silicate layers, for subsequent intercalation of an oligomer or polymer between the layers, thereby substantially increasing the interlayer (interlaminar) spacing between the adjacent silicate layers. The thus-treated, intercalated phyllosilicates, having interlayer spacings increased by at least 3 xc3x85, preferably at least 5 xc3x85, e.g., to an interlayer (interlaminar) spacing of at least about 10-25 xc3x85 and up to about 100 Angstroms, then can be exfoliated, e.g., the silicate layers are separated, e.g., mechanically, by high shear mixing. The individual silicate layers, when admixed with a matrix polymer, e.g., a polyamidexe2x80x94see U.S. Pat. Nos. 4,739,007; 4,810,734; and 5,385,776xe2x80x94have been found to substantially improve one or more properties of the polymer, such as mechanical strength, barrier properties and/or high temperature characteristics.
Exemplary prior art composites, also called xe2x80x9cnanocompositesxe2x80x9d, are disclosed in published PCT disclosure of Allied Signal, Inc. WO 93/04118 and U.S. Pat. No. 5,385,776, disclosing the admixture of individual platelet particles (exfoliated platelets) derived from intercalated layered silicate materials, with a polymer to form a polymer matrix having one or more properties of the matrix polymer improved by the addition of the exfoliated intercalate. As disclosed in WO 93/04118, the intercalate is formed (the interlayer spacing between adjacent silicate platelets is increased) by adsorption of a silane coupling agent or an onium cation, such as a quaternary ammonium compound, having a reactive group which is compatible with the matrix polymer. Such quaternary ammonium cations are well known to convert a highly hydrophilic clay, such as sodium or calcium montmorillonite, into an organophilic clay capable of sorbing organic molecules.
Maxfield U.S. Pat. No. 5,514,734 (""734) discloses intercalation of clay with both a coupling agent (silane, titanate or zirconate) and onium ions together with in-situ polymerization of a nylon polymer precursor, such as polymerizable nylon monomers, e.g., xcex5-caprolactam, capable of in-situ polymerization to form a polymer that is reactive with the coupling agent to tether the polymer to the clay platelets. In accordance with the present invention, a coupling agent-reacted and onium compound-intercalated layered silicate material is polymer melt processed for unexpectedly better dispersibility of the exfoliated platelets throughout a matrix polymer, particularly non-polar matrix polymers, such as polyolefins, especially polyethylene and/or polypropylene. In accordance with the present invention, the coupling agent preferably is not reactive with the matrix polymer, so that the matrix polymer is not tethered to the clay platelets. The Maxfield ""734 patent is hereby incorporated by reference for its disclosure of coupling agents useful in accordance with the present invention.
Edges of clay layered materials are replete with hydroxy groups (xe2x80x94OH) that make it extremely difficult to intercalate non-polar and low polarity oligomers and polymers. In accordance with the preferred embodiment of the present invention, as disclosed in co-pending application Ser. No. 09/516,136 filed Mar. 1, 2000, it has been found that by reacting the xe2x80x94OH groups at the edges of clay platelets with a coupling agent, to form coupling agent covalent bonds at the clay edges, the clay becomes much more receptive to intercalation of such non-polar and low polarity oligomers and polymers, particularly polyolefins such as ethylene and propylene homopolymers and copolymers. It should be understood, however, that it is not essential to react the layered material edges with a coupling agent in accordance with the present invention since polyolefin intercalant(s) can be intercalated without the coupling agent reaction, particularly when incorporating a relatively small percentage, e.g., about 0.1-10% by weight, preferably about 0.2% to about 3% by weight, more preferably about 1% to about 3%, most preferably about 1% to about 2% by weight of a maleic anhydride-modified polyolefin in addition to the polyolefin intercalant. To achieve the full advantage of the present invention, the maleic anhydride-modified polyolefin should have a weight average molecular weight of at least about 5,000, preferably at least about 10,000, more preferably at least about 40,000.
Useful coupling agents include those selected from the group consisting of silanes, titanates, aluminates, zirconates, and mixtures thereof, particularly the organosilanes, organotitanates, organoaluminates and/or organozirconates. The coupling agent(s) can be reacted with the xe2x80x94OH functionalities at the edges of the layered material platelets by contacting the layered material, before, during, or after onium ion intercalation, with the coupling agents in the form of a gas, neat liquid, finely divided (e.g., non-colloidal) solid, or solute in a solvent. While onium ion intercalation is preferred, it should be understood that onium ion intercalation also is not necessary in accordance with the present invention when a relatively small amount of maleic anhydride-modified polyolefin, e.g., 0.2% to 10%, based on the total weight of polyolefin and maleic anhydride-modified polyolefin contacting the clay, is incorporated into the clay together with the polyolefin. The concentration of coupling agent, when used, should be at least about 0.1%, preferably in the range of about 0.1% to about 10% by weight, more preferably in the range of about 0.5% to about 6% by weight, and most preferably about 1% to about 4% by weight, based on the dry weight of the layered material. The preferred coupling agents have a structure as follows: 
wherein x=Si, Ti, Zr or Al
wherein R1 is an organic radical, preferably an alkyl radical or an amine radical, bonded directly to the Si, Ti, Zr or Al atom (x) and at least one of R2, R3 and R4 is a radical containing a functionality, preferably an organic functionality, capable of a condensation reaction with a hydrogen from the xe2x80x94OH groups at the edges of the layered material, preferably selected from H, halogen, alkoxy, acyloxy and amine.
The xe2x80x94OH reaction of the coupling agent, e.g., silane, can be accomplished by either adding the silane to a dry onium-intercalated clay, i.e., organoclay, or by adding the silane to a water slurry of the organoclay, followed by removal of by-products and solvent during heat treatment. Alternatively, the silane also be added to the polymer-organoclay nanocomposite by integral blend methods. In this method, undiluted silane is added to the polymer either before or after introduction of the onium-intercalated clay or organoclay. It is preferable to add the silane before introduction of the clay because this allows for better dispersion and distribution of the silane into the polymer.
In addition to, or instead of, the platelet edge xe2x80x94OH reaction with a coupling agent, the layered material also is intercalated with onium ions, e.g., ammonium ions, having a general structure of: 
Where R1 is a C2-C22 alkyl chain, straight chain or branched, and R2, R3 and R4, same or different, is hydrogen or an alkyl aryl or alkyl moiety, preferably a is C1-C8 alkyl chain.
In accordance with an important feature of the present invention, the layered material is intercalated with a substantial majority of polyolefin, e.g., about 90% to about 99.8% by weight polyolefin, preferably a polypropylene homopolymer, and about 0.2% to about 10%, preferably about 1% to about 5%,more preferably about 1% to about 3% by weight maleic anhydride-modified polyolefin, based on the total weight of the intercalant oligomers or polymers and intercalated matrix polymer. The resulting polyolefin/modified polyolefin intercalated nanocomposite has improved mechanical properties and heat stability over traditional polyolefin-intercalated nanocomposites, it is theorized due to the combination of the polyolefin with a maleic anhydride modified polyolefin enabling more complete intercalation of the polyolefin intercalants between clay platelets for surprisingly better exfoliation and dispersibility of clay platelets and fewer, thinner tactoids.
The interlaminar spacing of adjacent layers (platelets) of the coupling agent-reacted layered material is expanded at least about 3 xc3x85, preferably at least about 5 xc3x85, to a basal spacing of at least about 10 xc3x85, preferably to at least about 15 xc3x85, and usually to about 18 xc3x85 in any manner known in the art, preferably by contacting the layered material with an onium ion spacing agent for subsequent intercalation with polyolefin and maleic anhydride-modified polyolefin oligomers or polymers. The optional onium ion may be primary, secondary, tertiary or quaternary and preferably is a long chain (C6+) onium ion spacing agent having at least one binding (ion-exchange) site capable of ion-exchanging or replacing Li+, Na+, K+, Ca+, Mg+2, or other inorganic cations that occur within the interlayer spaces between adjacent layers or platelets of the layered materials. The association of the layered material inorganic cations with the onium ion spacing agent via ion-exchange enables the conversion of the hydrophilic interior clay platelet surfaces to hydrophobic platelet surfaces. Therefore, oligomers or polymers can be easily intercalated between adjacent platelets of the layered material, e.g., smectite clay platelets, after onium ion intercalation.
In accordance with the preferred embodiment of the present invention, an olefin oligomer or polymer, such as polyethylene, polypropylene or copolymers thereof, having a weight average molecular weight between about 100 and about 5 million, preferably about 1,000 to about 500,000, and about 10% to about 90%, preferably about 25% to about 50% by weight of a maleic anhydride-modified polyolefin, having a weight average molecular weight of at least about 5,000, preferably at least about 10,000, is intercalated between adjacent platelets of the layered material, to form an intercalate concentrate. Alternatively, the layered material can be intercalated with the polyolefin and maleic anhydride-modified polyolefin directly with the matrix polymer containing both the polyolefin and maleic anhydride-modified polyolefin, after onium ion intercalation. Optionally, the intercalate concentrate is sheared to exfoliate the intercalate into a predominance of individual platelets. The concentration of intercalate, or exfoliate thereof, should be in the range of about 10-90% by weight, preferably 20-80%, more preferably 30-60% by weight in the concentrate. The concentrate is then mixed into a matrix polymer, comprising a polyolefin oligomer or polymer and a maleic anhydride-modified polyolefin oligomer or polymer, i.e., by direct compounding of the intercalated layered material with the polymers. The combination of matrix polymer polyolefin(s) and the initial formation of an intercalate and/or/exfoliate concentrate, results in a completely homogeneous dispersion of intercalated layered material and/or exfoliated platelets.
Maleic anhydride-modified polypropylene (MA-PP) oligomers and polymers are well known for use in making nanocomposites, as disclosed in Hasegawa, et al. Preparation And Mechanical Properties Of Polypropylenexe2x80x94Clay Hybrids Using A Maleic Anhydride-Modified Polypropylene Oligomer, Journal of Applied Polymer Science, Vol. 67, pages 87-92 (1998), hereby incorporated by reference. It has been found that the higher molecular weight maleic anhydride-modified polyolefins, having a weight average molecular weight of at least 10,000, preferably at least 40,000, provide much better mechanical properties, such as strength and temperature resistance. If the weight average molecular weight is too low, e.g., below about 5,000, the maleic anhydride-modified polyolefin will perform as a plasticizer and decrease the properties of the polyolefin in the nanocomposite; if the weight percentage of the maleic anhydride (measured as a weight of maleic anhydride only) is too high, e.g., above about 5% by weight, based on the weight of the maleic anhydride-modified polyolefin, the maleic anhydride-modified polyolefin will not be compatible with neat polyolefins; if too low, e.g., below about 0.2% by weight, the resin has limited compatibility with the modified montmorillonite.
The maleic anhydride-modified polypropylene (MA-PP) oligomer described in the Hasegawa et al. article from Sanyo Chemical Industries, having an acid value of 52 mg KOH/g, a softening temperature of 145xc2x0 C., and a weight average molecular weight of about 30,000, is suitable in accordance with the present invention. However, any other available maleic anhydride-reacted polyolefin, preferably polypropylene, also is suitable in accordance with the principles of the present invention. The Hasegawa et al. article teaches using a minimum ratio of maleic anhydride-modified polypropylene (MA-PP) to polypropylene homopolymer (PP) of 7% by weight MA-PP to 93% by weight PP, when the combination is used to form a nanocomposite. In accordance with the present invention, it has been found that best results are achieved by incorporating a matrix polymer combination of a polyolefin and a maleic anhydride-modified polyolefin, having about 0.2% to about 10% by weight maleic anhydride-modified polyolefin, preferably about 1% to about 5% by weight maleic anhydride-modified polyolefin, more preferably about 1% to about 3% by weight maleic anhydride-modified polyolefin and polyolefin combined with the clay.
Optionally, the nanocomposite concentrate can be sheared to exfoliate up to 100% of the tactoids or platelet clusters into individual platelets, preferably such that more than 80%; or more than 90% by weight of the layered material can be completely exfoliated into single platelet layers. Quick, easy, and completely homogeneous dispersion of the co-intercalated layered material in a polyolefin matrix polymer is achieved and the resulting nanocomposite has unexpectedly easy polymer intercalation and homogeneous dispersion of the intercalate and/or exfoliate throughout the matrix polymer. Additional matrix polymer, particularly a polyolefin, can be added after shearing so that the added matrix polymer, particularly polyolefin, is not degraded by substantial shearing and is subjected to limited high temperature degradation.
The intercalates of the present invention preferably are dispersed uniformly into a matrix polymer that is a combination of polypropylene and maleic anhydride-modified polypropylene to form a polymer/clay intercalate-containing nanocomposite and/or polymer/exfoliate-containing nanocomposites by direct compounding of the polyolefin-intercalated clay with sufficient matrix oligomers or matrix polymers to form a concentrate, that can later be mixed with additional matrix polymer, without subsequent polymer-degrading shear, to form a nanocomposite. The intercalate concentrate can be directly compounded with the additional pristine matrix polymer, preferably the same as the polymer intercalant, to form a nanocomposite easily, while achieving a nanocomposite material with homogeneously dispersed platelets. The intercalate of the present invention can also be prepared with polymer solutions as well as polymer emulsions. This processing route will eliminate the melt compounding process and reduce thermal degradation of the polymer intercalant and the matrix polymer.
In accordance with a preferred embodiment of the present invention, intercalates are prepared by contacting a phyllosilicate with a monomeric onium ion spacing agent compound. To achieve the full advantage of the present invention, the onium ion should include at least one long chain radical (C6+) that may be aliphatic, straight or branched chain, or aralkyl. Exemplary of such suitable C6+ onium ion molecules include primary, secondary, tertiary or quaternary ammonium ions, sulfonium ions, phosphonium ions, oxonium ions, or any ion of an element in Groups V or VI of the periodic table of elements.
In accordance with an important feature of the preferred embodiment of the present invention, best results are achieved by mixing the layered material with the onium ions, e.g., C6+ onium ion spacing coupling agent-reacted, in a concentration of at least about 2% by weight, preferably at least about 5% by weight onium ion compound, more preferably at least about 10% by weight onium ion compound, and most preferably about 20% to about 50% by weight, based on the weight of onium ion compound and carrier (e.g., water, with or without an organic solvent for the onium ion compound) to achieve better sorption of the onium ion spacing agent compound between the platelets of the layered material. Regardless of the concentration of onium ion compound in the onium ion intercalating composition, the weight ratio of polymer intercalant:layered material should be at least 1:20, preferably at least 1:10, more preferably at least 1:5, and most preferably about 1:4 to achieve sufficient oligomer or polymer intercalation of polyolefin and maleic anhydride-modified polyolefin intercalants between adjacent inner surfaces of adjacent platelets of the layered material. The optional, preferred onium ion spacing agent compound ion-exchanged with and bonded to (or complexed with) the aluminosilicate platelets via ion-exchange causes surprisingly easy intercalation of the polyolefin oligomer or polymer intercalants.
Due to the low polarity of general polyolefin resins, a compatiblizer such as a maleic anhydride-modified polyolefin is needed to achieve good intercalation and exfoliation of a polyolefin-intercalated layered silicate material, such as a montmorillonite clay, in the matrix resin. However, the intercalation and exfoliation of the layered silicate material in a polyolefin matrix polymer can also be achieved without a compatibilizer, such as a maleic anhydride-modified polyolefin if the polyolefin has sufficient polarity. In addition, the intercalation and exfoliation of the layered silicate material can be achieved by using a maleic anhydride-modified polyolefin as the matrix resin. For some polyolefins, such as ethylene vinyl acetate (EVA), the polarity is high enough for the layered silicate material to be intercalated and exfoliated, without the need for the maleic anhydride-modified polyolefin. In this case, no additional compatibilizer is needed to form nancomposites.
The co-intercalation of the combination of a polyolefin and a maleic anhydride-modified polyolefin to form a concentrate intercalate or a concentrate exfoliate, in accordance with the preferred embodiment of the present invention, provides an intercalate or exfoliate concentrate that can be added, particularly by direct compounding (mixing the intercalate directly into a matrix polymer melt, preferably a polyolefin matrix polymer melt that is the same as the intercalated combination of the polyolefin and maleic anhydride-modified polyolefin) of the intercalate with a matrix oligomer or matrix polymer that is a combination of the same polyolefin and the same maleic anhydride-modified polyolefin that were intercalated between adjacent platelets of the layered silicate material. The co-intercalation of the preferred combination to form a concentrate intercalate composition or a concentrate exfoliate composition can also be formed through either a solution or emulsion intercalation process route. The intercalate and/or exfoliate concentrate, added to the matrix polymer, improved a number of properties of the matrix polymer, including tensile properties, dimensional stability, ductility, gas-impermeability, and the like.
Whenever used in this Specification, the terms set forth shall have the following meanings:
xe2x80x9cLayered Materialxe2x80x9d shall mean an inorganic material, such as a smectite clay mineral, that is in the form of a plurality of adjacent, bound layers and has a thickness, for each layer, of about 3 xc3x85 to about 50 xc3x85, preferably about 10 xc3x85.
xe2x80x9cPlateletsxe2x80x9d shall mean individual layers of the Layered Material.
xe2x80x9cIntercalatexe2x80x9d or xe2x80x9cIntercalatedxe2x80x9d shall mean a Layered Material that includes a polyolefin oligomer or polyolefin polymer and a maleic anhydride-modified polyolefin oligomer or polymer disposed between adjacent platelets of the Layered Material to increase the interlayer spacing between the adjacent platelets at least 3 xc3x85, preferably at least 5 xc3x85, to an interlayer spacing, for example, of at least about 10 xc3x85, preferably at least about 15 xc3x85;
xe2x80x9cOptional Coupling Agent-Treatedxe2x80x9d or xe2x80x9cOptional Coupling Agent-Treatmentxe2x80x9d or xe2x80x9cOptional Coupling Agent-Reactedxe2x80x9d shall mean the optional contact of a layered material with a coupling agent, e.g., a silane coupling agent, a titanate coupling agent, a zirconate coupling agent and/or an aluminate coupling agent to produce a condensation reaction between the coupling agent and xe2x80x94OH radicals at the edges of the platelets of the Layered Material.
xe2x80x9cIntercalationxe2x80x9d shall mean a process for forming an Intercalate.
xe2x80x9cOnium Ion Spacing Agentxe2x80x9d or xe2x80x9cOnium Ion Compoundxe2x80x9d shall mean an organic compound that includes a positively charged atom selected from the group consisting of a nitrogen atom, a phosphorous atom, a sulfur atom or an oxygen atom, preferably a quaternary ammonium compound, and when dissolved in water and/or an organic solvent, an anion dissociates from the onium ion spacing agent leaving an onium cation that can ion-exchange with a silicate platelet exchangeable cation, e.g., Na+, Ca+2, Li+, Mg+2, or K+, thereby binding to the silicate platelet inner surface.
xe2x80x9cCo-Intercalationxe2x80x9d shall mean a process for forming an intercalate by intercalation of an oligomer or polymer of a polyolefin, e.g., polypropylene, and, at the same time or separately, intercalation of a maleic anhydride-modified polyolefin polymer, or intercalation of a maleic anhydride-modified polyolefin oligomer.
xe2x80x9cConcentratexe2x80x9d shall mean an intercalate or exfoliate, formed by the Co-Intercalation of a Layered Material to form a concentrate comprising 10-90% polyolefin oligomer or polymer, same as or different than the matrix polymer, and 10-90% polyolefin Intercalate or polyolefin exfoliate.
xe2x80x9cIntercalating Carrierxe2x80x9d shall mean a carrier comprising water and/or an organic solvent used with the intercalant oligomers or polymers to form an Intercalating Composition capable of achieving Intercalation of the polyolefin co-intercalants and, at the same time or separately, intercalation of the oligomers or polymers between platelets of the Layered Material.
xe2x80x9cIntercalating Compositionxe2x80x9d or xe2x80x9cIntercalant Compositionxe2x80x9d shall mean a composition comprising a Layered Material together with a polyolefin and/or a maleic anhydride-modified polyolefin, with or without an Intercalating Carrier.
xe2x80x9cExfoliatexe2x80x9d or xe2x80x9cExfoliatedxe2x80x9d shall mean individual platelets of a Co-Intercalated Layered Material or tactoids or clusters of individual platelets, e.g., 2-10 platelets, preferably 2-5 platelets, that are smaller in total thickness than the non-exfoliated Layered Material, dispersed as individual platelets or tactoids throughout a carrier material, such as water, a polymer, an alcohol or glycol, or any other organic solvent, or throughout a matrix polymer.
xe2x80x9cExfoliationxe2x80x9d shall mean a process for forming an Exfoliate from an Intercalate.
xe2x80x9cMatrix Polymerxe2x80x9d shall mean an oligomer or polymer, that the Intercalate or Exfoliate is dispersed within to improve the mechanical strength, thermal resistance, and/or the gas (O2) impermeability of the Matrix Polymer, preferably a polyolefin homopolymer or polyolefin copolymer, particularly polyethylene, polypropylene or copolymers thereof.
In brief, the present invention is directed to intercalated layered materials prepared by intercalation of a polyolefin, preferably polypropylene, and optionally a maleic anhydride-modified polyolefin, preferably a maleic anhydride-modified polypropylene oligomer or polymer, between the planar layers of a swellable layered material, such as a phyllosilicate, preferably a smectite clay, to form a concentrate. The concentrate can be subjected to substantial sheer to exfoliate a majority of the intercalate; preferably at least 80% by weight of the intercalated layered material is exfoliated into individual platelets and/or tactoids of 2-5 platelet layers. After exfoliation, additional matrix polyolefin polymer can be added to avoid additional shear, thereby avoiding polymer degradation of the matrix polymer added to the concentrate.
The present invention is directed to a method of preparing intercalated layered materials, prepared by intercalation of a polyolefin oligomer or polymer and optionally a maleic anhydride-modified polyolefin oligomer or polymer into the galleries of the layered material to form an intercalate concentrate composition that provides new and unexpected dispersibility throughout a matrix polymer, particularly a matrix oligomer or matrix polymer that is a combination of polypropylene, and a maleic anhydride-modified polypropylene.
The present invention also is directed to the intercalates and exfoliates prepared from the intercalate or intercalate concentrate compositions. When the concentrate is mixed with a melt of the combination of a polyolefin and a maleic anhydride-modified polyolefin matrix oligomer or matrix polymer after shearing, (preferably the same polymer as the predominant intercalant polymer), the layered materials are unexpectedly easily dispersed throughout the matrix oligomers or matrix polymers, without degradation by shearing of the added matrix polymer.
The layered material is intercalated, preferably by first contacting the layered material with an onium ion spacing agent and simultaneously or thereafter adding the melted polyolefin oligomer intercalant or melted polyolefin polymer intercalant to the onium ion-intercalated layered material, such as by direct compounding of the layered material and the melted oligomer(s) or polymer(s) intercalant in an extruder, to intercalate the onium ion and melted polyolefin oligomer(s) or polymer(s) between adjacent phyllosilicate platelets and optionally separate (exfoliate) the layered material into individual platelets. The present invention also is directed to the intercalates and exfoliates prepared from the intercalate or intercalate concentrate compositions. Melt compounding or solution/emulsion intercalation processes can be used to prepare the compositions.
Addition of the intercalate to a polymer melt enhances one or more properties, such as strength, temperature resistance, dimensional stability, ductility, and/or gas impermeability of the polymer; or mixing the intercalate with a carrier or solvent material maintains and/or increases viscosity and thixotropy of the carrier material. The intercalate is easily, homogeneously and uniformly dispersed throughout a matrix oligomer or matrix polymer combination of a polyolefin and a maleic anhydride-modified polyolefin and provides new and unexpected strength properties to non-polar matrix polymers by virtue of the unexpectedly homogeneous dispersibility of the co-intercalate and/or exfoliate throughout a low polarity or non-polar matrix oligomer or polymer, particularly a combination of polypropylene and maleic anhydride-modified polypropylene.
To form the intercalated and exfoliated materials of the present invention, the layered material, e.g., the phyllosilicate, should be intercalated with a polyolefin oligomer or polymer, preferably polyethylene or polypropylene, and thereafter melt compounded with a matrix oligomer or matrix polymer combination of a polyolefin, preferably polyethylene or polypropylene, and with an oligomer or polymer of a maleic anhydride-modified polyolefin, preferably polyethylene or polypropylene.
In a preferred embodiment, the interlaminar spacing between adjacent platelets of a layered silicate material, e.g., a phyllosilicate, is expanded for easier co-intercalation by a first treatment with a coupling agent followed by intercalation and ion-exchange of onium ions between the aluminosilicate platelets, prior to or simultaneously with intercalation of the polyolefin oligomer(s) or polymer(s). It should be understood that the oligomer or polymer intercalant(s) can be intercalated between and complexed to the internal platelet faces by other well known mechanisms, such as the dipole/dipole (direct intercalation of the oligomer or polymer) method disclosed in this Assignee""s U.S. Pat. Nos. 5,880,197 and 5,877,248, hereby incorporated by reference; and by the acidification techniquexe2x80x94by substitution with hydrogen (ion-exchanging the interlayer cations with hydrogen by use of an acid or ion-exchange resin) as disclosed in the Deguchi U.S. Pat. No. 5,102,948, and in the Pinnavaia, et al. U.S. Pat. No. 5,853,886, both patents hereby incorporated by reference.
The onium ion spacing agent is introduced into the layered material galleries in the form of a solid or liquid composition (neat or aqueous, with or without an organic solvent, e.g., an aliphatic hydrocarbon, such as heptane to, if necessary, aid to dissolve the onium ion compound) having an onium ion spacing agent concentration sufficient to provide an onium ion concentration of about 5% to about 10% by weight of the clay (90-95% water) and the onium ion compound is dissolved in the clay slurry water, preferably at a molar ratio of onium ions to exchangeable interlayer cations of at least about 0.25:1, more preferably at least about 0.5:1, most preferably at least about 1:1. The onium ion-intercalated clay then is separated from the water easily, since the clay is now hydrophobic, and dried in an oven to less than 5% water, preferably bone dry, before being compounded (co-intercalated) with the oligomers or polymers, for co-intercalation of the oligomers or polymers and homogeneous platelet dispersion. The optional onium ion spacing agent compound can be added as a solid with the addition to the layered material onium ion compound blend of preferably at least about 20% by weight water, more preferably at least about 30% by weight water or more, based on the dry weight of the layered material. Preferably about 30% to about 50% water, more preferably about 30% to about 40% by weight water, based on the dry weight of the layered material, is included in the onium ion intercalating composition, so that less water is sorbed by the intercalate, thereby necessitating less drying energy after onium ion intercalation.
The optional, but preferred onium ion spacing agent cations intercalated via ion-exchange into the interlayer spaces between adjacent layered material platelets are primary, secondary, tertiary or quaternary onium ions having the following preferred structure: 
wherein Xxe2x95x90N, P, S, or O; and
wherein R1, R2, R3 and R4 are H or organic moieties, such as linear or branched alkyl, aryl or aralkyl moieties having 1 to a bout 24 carbon atoms.
The more preferred C6+ onium ions are preferably quaternary ammonium ions having Formula 1, as follows: 
Wherein R1 is a long chain alkyl moiety ranging from C6 to C24, straight or branched chain, including mixtures of long chain moieties, i.e., C6, C8, C10, C12, C14, C16, C18, C20, C22 and C24, alone or in any combination; and R2, R3 and R4 are moieties, same or different, selected from the group consisting of H, alkyl, benzyl, substituted benzyl, e.g., straight or branched chain alkyl-substituted and halogen-substituted; ethoxylated or propoxylated alkyl; ethoxylated or propoxylated benzyl, e.g., 1-10 moles of ethoxylation or 1-10 moles of propoxylation.
Additional useful multi-charged spacing/coupling agents include for example, tetra-, tri-, and di-onium species such as tetra-ammonium, tri-ammonium, and di-ammonium (primary, secondary, tertiary, and quaternary), -phosphonium, -oxonium, or -sulfonium derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines, esters, alcohols and sulfides. Illustrative of such materials are di-onium compounds of the formula:
R1xe2x80x94X+xe2x80x94Rxe2x80x94Y+
where X+ and Y+, same or different, are ammonium, sulfonium, phosphonium, or oxonium radicals such as
xe2x80x83xe2x80x94NH(CH3)2+, xe2x80x94NH2(CH3)+, xe2x80x94N(CH3)3+,
xe2x80x94N(CH3)2(CH2CH3)+, xe2x80x94N(CH3)(CH2CH3)2+, xe2x80x94S(CH3) 2 +
xe2x80x94S(CH3)2+, xe2x80x94P(CH3)3+, xe2x80x94NH3+,
and the like; R is an organic spacing, backbone radical, straight or branched, preferably having from 2 to 24, more preferably 3 to 10 carbon atoms, in a backbone organic spacing molecule covalently bonded at its ends to charged N+, P+, S+ and/or O+ cations and R1 can be hydrogen, or an alkyl radical of 1 to 22 carbon atoms, linear or branched, preferably having at least 6 carbon atoms. Examples of R include substituted or unsubstituted alkylene, cycloalkenylene, cycloalkylene, arylene, alkylarylene, either unsubstituted or substituted with amino, alkylamino, dialkylamino, nitro, azido, alkenyl, alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkylthio, alkyl, aryloxy, arylalkylamino, alkylamino, arylamino, dialkylamino, diarylamino, aryl, alkylsufinyl, aryloxy, alkylsulfinyl, alkylsulfonyl, arylthio, arylsulfinyl, alkoxycarbonyl, arylsulfonyl, or alkylsilane. Examples of R1 include non-existent; H; alkyl having 1 to 22 carbon atoms, straight chain or branched; cycloalkenyl; cycloalkyl; aryl; alkylaryl, either unsubstituted or substituted or substituted with amino, alkylamino, dialkylamino, nitro, azido, alkenyl, alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkylthio, alkyl, aryloxy, arylalkylamino, alkylamino, arylamino, dialkylamino, diarylamino, aryl, alkylsufinyl, aryloxy, alkylsulfinyl, alkylsulfonyl, arylthio, arylsulfinyl, alkoxycarbonyl, arylsulfonyl, or alkylsilane. Illustrative of useful R groups are alkylenes, such as methylene, ethylene, octylene, nonylene, tert-butylene, neopentylene, isopropylene, sec-butylene, dodecylene and the like; alkenylenes such as 1-propenylene, 1-butenylene, 1-pentenylene, 1-hexenylene, 1-heptenylene, 1-octenylene and the like; cycloalkenylenes such as cyclohexenylene, cyclopentenylene and the like; alkanoylalkylenes such as butanoyl octadecylene, pentanoyl nonadecylene, octanoyl pentadecylene, ethanoyl undecylene, propanoyl hexadecylene and the like; alkylaminoalkylenes, such as methylamino octadecylene, ethylamino pentadecylene, butylamino nonadecylene and the like; dialkylaminoalkylene, such as dimethylamino octadecylene, methylethylamino nonadecylene and the like; arylaminoalkylenes such as phenylamino octadecylene, p-methylphenylamino nonadecylene and the like; diarylaminoalkylenes, such as diphenylamino pentadecylene, p-nitrophenyl-pxe2x80x2-methylphenylamino octadecylene and the like; alkylarylaminoalkylenes, such as 2-phenyl-4-methylamino pentadecylene and the like; alkylsulfinylenes, alkylsulfonylenes, alkylthio, arylthio, arylsulfinylenes, and arylsulfonylenes such as butylthio octadecylene, neopentylthio pentadecylene, methylsulfinyl nonadecylene, benzylsulfinyl pentadecylene, phenylsulfinyl octadecylene, propylthiooctadecylene, octylthio pentadecylene, nonylsulfonyl nonadecylene, octylsulfonyl hexadecylene, methylthio nonadecylene, isopropylthio octadecylene, phenylsulfonyl pentadecylene, methylsulfonyl nonadecylene, nonylthio pentadecylene, phenylthio octadecylene, ethyltio nonadecylene, benzylthio undecylene, phenethylthio pentadecylene, sec-butylthio octadecylene, naphthylthio undecylene and the like; alkoxycarbonylalkylenes such as methoxycarbonylene, ethoxycarbonylene, butoxycarbonylene and the like; cycloalkylenes such as cyclohexylene, cyclopentylene, cyclooctylene, cycloheptylene and the like; alkoxyalkylenes such as methoxymethylene, ethoxymethylene, butoxymethylene, propoxyethylene, pentoxybutylene and the like; aryloxyalkylenes and aryloxyarylenes such as phenoxyphenylene, phenoxymethylene and the like; aryloryalkylenes such as phenoxydecylene, phenoxyoctylene and the like; arylalkylenes such as benzylene, phenthylene, 8-phenyloctylene, 10-phenyldecylene and the like; alkylarylenes such as 3-decylphenylene, 4-octylphenylene, 4-nonylphenylene and the like; and polypropylene glycol and polyethylene glycol substituents such as ethylene, propylene, butylene, phenylene, benzylene, tolylene, p-styrylene, p-phenylmethylene, octylene, dodecylene, octadecylene, methoxyethylene, moieties of the formula xe2x80x94C3H6COOxe2x80x94, xe2x80x94C5H10COOxe2x80x94, xe2x80x94C7H10COOxe2x80x94, xe2x80x94C7H14COOHxe2x80x94, xe2x80x94C9H18COOxe2x80x94, xe2x80x94C11H22COOxe2x80x94, xe2x80x94C13H26COOxe2x80x94, xe2x80x94C15H30COOxe2x80x94, and xe2x80x94C17H34COOxe2x80x94and xe2x80x94Cxe2x95x90C(CH3)COOCH2CH2xe2x80x94, and the like. Such tetra-, tri-, and di-ammonium, -sulfonium, -phosphonium, -oxonium; ammonium/sulfonium; ammonium/phosphonium; ammonium/oxonium; phosphonium/oxonium; sulfonium/oxonium; and sulfonium/phosphonium radicals are well known in the art and can be derived from the corresponding amines, phosphines, alcohols or ethers, and sulfides.
The preferred multi-charged spacing/coupling agent compounds are multi-onium ion compounds that include at least two primary, secondary, tertiary or quaternary ammonium, phosphonium, sulfonium, and/or oxonium ions having Formula 2, as follows: 
wherein R is an alkylene, aralkylene or substituted alkylene charged atom spacing moiety, preferably ranging from C3 to C24, more preferably about C3 to C6 for relatively high charge density (150 milliequivalents/100 grams C.E.C. to 70 milliequivalents/100 grams C.E.C.) layered materials; and preferably from C6 to C12 for medium to low charge density (70 milliequivalents/100 grams C.E.C. to 30 milliequivalents/100 grams C.E.C.) layered materials. R can be straight or branched chain, including mixtures of such moieties, i.e., C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C21, C22, C23 and C24, alone or in any combination; and R1, R2, R3 and R4 are moieties, same or different, selected from the group consisting of hydrogen, alkyl, aralkyl, benzyl, substituted benzyl, e.g., straight or branched chain alkyl-substituted and halogen-substituted; ethoxylated or propoxylated alkyl; ethoxylated or propoxylated benzyl, e.g., 1-10 moles of ethoxylation or 1-10 moles of propoxylation. Z1 and Z2, same or different, may be non-existent, or may be any of the moieties described for R1, R2, R3 or R4. Also, one or both of Z1 and Z2 may include one or more positively charged atoms or onium ion molecules.
Any swellable layered material that sufficiently ion-exchanges with the onium ion spacing agent at the internal platelet faces to increase the interlayer spacing between adjacent phyllosilicate platelets at least about 3 xc3x85, preferably at least about 5 xc3x85, can be used in the practice of this invention. Useful swellable layered materials include phyllosilicates, such as smectite clay minerals, e.g., montmorillonite, particularly sodium montmorillonite; magnesium montmorillonite and/or calcium montmorillonite; nontronite; beidellite; volkonskoite; hectorite; saponite; sauconite; sobockite; stevensite; svinfordite; vermiculite; and the like. Other useful layered materials include micaceous minerals, such as illite and mixed layered illite/smectite minerals, such as rectorite, tarosovite, ledikite and admixtures of illites with the clay minerals named above.
Preferred swellable layered materials are phyllosilicates of the 2:1 type having a negative charge on the layers ranging from about 0.15 to about 0.9 charges per formula unit and a commensurate number of exchangeable metal cations in the interlayer spaces. Most preferred layered materials are smectite clay minerals such as montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite, sobockite, stevensite, and svinfordite.
As used herein the xe2x80x9cinterlayer spacingxe2x80x9d refers to the distance between the internal faces of the adjacent layers as they are assembled in the layered material before any delamination (exfoliation) takes place. The preferred clay materials generally include interlayer cations such as Na+, Ca+2, K+, Mg+2, NH4+ and the like, including mixtures thereof, particularly Na+.
The amount of onium ion spacing agent intercalated into the swellable layered materials, in order that the intercalated layered material platelet surfaces sufficiently complex or bond via ion-exchange to the onium ion spacing agent molecules such that the layered material may be sufficiently spaced for easy intercalation of an oligomer or polymer may vary substantially between about 2%, preferably at least about 10%, and up to about 80%, based on the dry weight of the layered material. In the preferred embodiments of the invention, amounts of onium ion employed, with respect to the dry weight of layered material being intercalated, will preferably range from about 8 grams of onium ion spacing agent compound: 100 grams of layered material (dry basis), preferably at least about 10 grams of onium ion spacing agent compound:100 grams of layered material to about 80-90 grams onium ion spacing agent compound:100 grams of layered material. More preferred amounts are from about 20 grams of onium ion spacing agent compound:100 grams of layered material to about 60 grams of onium ion spacing agent compound:100 grams of layered material (dry basis).
The polyolefin oligomer or polymer intercalant, and optionally a maleic anhydride-modified polyolefin oligomer or polymer intercalant, may be introduced into (sorbed within) the interlayer spaces of the layered material in a number of ways. In one method of intercalating the oligomer or polymer intercalants between adjacent platelets of the layered material, the layered material is slurried in water, e.g., at 5-20% by weight layered material and 80-95% by weight water, and an onium ion compound is dissolved in the water in which the layered material is slurried. If necessary, the onium ion compound can be dissolved first in an organic solvent, e.g., propanol. The layered material then is separated from the slurry water and dried prior to compounding, preferably melt compounding, with the oligomer or polymer intercalants (or co-intercalants) for intercalation of the polyolefin and, optionally, the maleic anhydride-modified polyolefin oligomer or polymer co-intercalant, to form the nanocomposite material in a concentrated form in polyolefin and maleic anhydride-modified polyolefin matrix oligomers or matrix polymers.
The intercalates and exfoliates can also be prepared through solution/emulsion processes. Optionally, the onium ion-intercalated layered material can be first intercalated with the polyolefin, prior to adding the matrix polymer, comprising both a polyolefin and a maleic anhydride-modified polyolefin or only the maleic anhydride-modified polyolefin, and then intercalated with the maleic anhydride-modified polyolefin from the matrix polymer, since regardless of the amount of polyolefin initially intercalated, some maleic anhydride-modified polyolefin will also be intercalated into the layered material from the matrix polymer. Optionally, the onium ion-intercalated layered material can be first intercalated with the maleic anhydride-modified pololefin, prior to adding the matrix polymer, comprising both a polyolefin and a maleic anhydride-modified polyolefin or only the polyolefin. In this case, it is preferred to limit the layered silicate material: maleic anhydride-modified polyolefin weight ratio to less than 1:2 to ensure a low (xe2x89xa610% by weight) concentration of maelic anhydride-modified polyolefin in the final nanocomposite. A layered silicate material intercalated with only the maleic anhydride-modified polyolefin (no polyolefin) can be easily dispersed into a polyolefin matrix resin (oligomer or polymer) to co-intercalate the polyolefin and form the nanocomposite.
The polyolefins can be intercalated into layered silicate materials by the emulsion process (as opposed to the melt compounding process) by vigorously mixing the polyolefin and/or the maleic anhydride-modified polyolefin with an emulsifier, such as non-ionic, cationic and/or anionic emulsifier. Cationic emulsifiers are preferred simply due to their good compatibility with montmorillonite clays. Some cationic emulsifiers, such as octadecyl amine, are most preferred, since they also function as montmorillonite surface modifiers (onium ions). In general, the low molecular weight, highly volatile emulsifiers are not preferred in the invention, due to a lessening of the final nanocomposite properties.
The coupling agent may be reacted with the layered material, preferably in an amount of about 2-4% by weight, based on the weight of the layered material, before or after (or simultaneously with) the onium ion-exchange intercalation. Preferred reaction conditions (which may vary considerably) include a temperature of about 70-75xc2x0 C. , a pH of about 3-5, to completion of the reaction. The coupling agent reaction can be performed in a slurry media or dry blending conditions. These lower reaction temperatures are preferred to allow the coupling agent to react at edge hydroxy groups more homogeneously over the entire layered material edges. In addition, the coupling agent may be introduced to the layered silicate in situ during the polymer melt compounding process. In a preferred method of intercalating the polymer, the coupling agent reacted and onium ion-treated layered material is intimately mixed with the polymer, e.g., by extrusion or pug milling, to form an intercalating composition comprising the coupling agent-reacted/onium ion-intercalated layered material and the intercalant polymer. In a preferred method of intercalating the oligomer or polymer intercalant, a coupling-agent reacted and onium ion-exchanged layered material is intimately mixed with a melt of the polymer co-intercalants, e.g., by extrusion or pug milling, to form an intercalating composition comprising a coupling agent-reacted/onium ion-intercalated layered material and a melt of the co-intercalant polyolefin and maleic anhydride-modified matrix oligomers or matrix polymers to form a co-intercalated concentrate composition for later dilution by the addition of matrix oligomers or matrix polymers to form the nanocomposite.
The coupling agent-treated layered material and onium ion intercalating composition preferably contains at least about 5% by weight, more preferably at least about 10% by weight onium ion compound, based on the dry weight of the coupling agent-treated layered material, so that the resulting onium ion-intercalated (ion-exchanged) layered material has interior platelet surfaces that are sufficiently hydrophobic and sufficiently spaced for co-intercalation of the polyolefin and maleic anhydride-modified polyolefin oligomers or polymers. The amount of the coupling agent, when used, should be at least 0.1% by weight, based on the dry weight of the layered material, preferably in the range of 0.5% to 60% by weight, based on the dry weight of the layered material. The onium ion carrier (preferably water, with or without an organic solvent) can be added by first solubilizing or dispersing the onium ion compound in the carrier; or a dry onium ion compound and relatively dry coupling agent-treated phyllosilicate (preferably containing at least about 4% by weight water) can be blended and the intercalating carrier added to the blend, or to the phyllosilicate prior to adding the dry onium ion. When intercalating the phyllosilicate with onium ions in slurry form (e.g., 900 pounds water, 100 pounds phyllosilicate, 100 pounds onium ion compound), the amount of water can vary substantially, e.g., from about 4% by weight, preferably from a minimum of at least about 30% by weight water, with no upper limit to the amount of water in the intercalating composition (the phyllosilicate intercalate is easily separated from the intercalating composition due to its hydrophobicity after onium ion treatment).
Alternatively, the onium ion intercalating carrier, e.g., water, with or without an organic solvent, can be added directly to the coupling agent-treated phyllosilicate prior to adding the onium ion compound, either dry or in solution. Ion-exchange of the onium ion compound molecules may be performed by exposing the coupling agent-treated layered material to a dry or liquid onium ion compound in the onium ion intercalating composition containing at least about 2% by weight, preferably at least about 5% by weight onium ion compound, more preferably at least about 10% onium ion compound, based on the dry weight of the layered material.
In accordance with another method of intercalating the onium ions and the polyolefin oligomer(s) or polymer(s) between the platelets of the coupling agent-reacted layered material, the layered material, preferably containing at least about 4% by weight water, more preferably about 10% to about 15% by weight water, is blended with water and/or organic solvent solution of an onium ion spacing agent compound in a ratio sufficient to provide at least about 5% by weight, preferably at least about 10% by weight onium ion compound, based on the dry weight of the layered material. The onium ion compound can be intercalated and ion-exchanged into a coupling agent-reacted layered material simultaneously with onium ion spacing agent contact with the layered material and simultaneously with the intercalation of the preferred polyolefin intercalant (and optionally a maleic anhydride-modified co-intercalant) oligomer(s) or polymer(s); or, the intercalant oligomer(s) or polymer(s) may be intercalated without or after coupling agent-reaction and intercalation of the onium ion spacing agent. In preferred embodiment, the dry onium ion-intercalated clay is extruded with a melt of the intercalant oligomer(s) or polymer(s) for direct compounding, with intercalation of the intercalant oligomer(s) or polymer(s) melt into the layered material with or without the coupling agent-reaction.
In accordance with a preferred embodiment of the present invention, the coupling agent-reacted/onium ion-intercalated (ion-exchanged) layered material can be intercalated with oligomer or polymer by direct melt compounding in an extruder and then the intercalate is dispersed into a combination of a melt-processible, preferably polyolefin, matrix oligomer or polymer, and a melt-processible maleic anhydride-modified oligomer or polymer, to form the nanocomposite. The matrix oligomers or matrix polymers for use in this embodiment of the process of this invention comprise a vinyl polymer or copolymer, particularly a polypropylene homopolymer having a melt flow index of preferably about 0.5 to about 60, more preferably about 5-10. The matrix polymer is added to the concentrate of co-intercalated layered material without extrusion of the added matrix polymer, after extruding the layered material with a melt of the polyolefin and maleic anhydride-modified polyolefin to form the nanocomposite concentrate in an extruder. The preferred matrix polyolefin oligomer or polymer preferably includes from at least about 10 to about 100 recurring monomeric units. In the most preferred embodiments of this invention, the number of recurring units is such that the matrix polymer has a melt index of from about 0.01 to about 12 grams per 10 minutes at the processing temperature.
The most preferred thermoplastic homopolymers and copolymer matrix polymers for forming nanocomposites with the coupling agent-reacted onium ion/polymer co-intercalated layered materials of the present invention are polymers formed by polymerization of alpha-beta-unsaturated monomers of the formula:
R2R3Cxe2x95x90CH2
wherein:
R2 and R3 are the same or different and are cyano, phenyl, carboxy, alkylester, halo, alkyl, or alkyl substituted with one or more chloro or fluoro, or hydrogen atoms. Illustrative of such preferred homopolymers and copolymers are homopolymers and copolymers of ethylene, propylene, vinyl alcohol, acrylonitrile, vinylidene chloride, esters of acrylic acid, esters of methacrylic acid, chlorotrifluoroethylene, vinyl chloride and the like. Preferred are poly(propylene), propylene copolymers, poly(ethylene) and ethylene copolymers. More preferred are homopolymers of poly(ethylene) and poly(propylene), and block and random copolymers thereof, especially polypropylene.
The following polyolefins and olefin copolymers are all useful as non-polar polyolefin and maleic anhydride-modified polyolefin intercalants, and as matrix polymers in accordance with the present invention.
Polyolefin homopolymers, including high-modulus homopolymers, contain only the olefin monomer in the polymer chain. The homopolymer provides stiffness and toughness but exhibits low impact strength at low temperatures, and clarity is too low for some applications. All three types of polyolefins, e.g., polyethylene, crystalline, amorphous, and elastomeric, are suitable as intercalants in accordance with the present invention. Polyolefin copolymers, such as ethylene-vinyl acetate (EVA), poly(4-methylpentene-1), and ethylene/xcex1-olefin copolymers, contain one or more different types of monomers in the polymer chain. Random copolymers are used in applications requiring higher clarity or a lower melting point, and impact copolymers are used in automotive and other applications that require high impact resistance at low temperatures. Thermoplastic olefins and thermoplastic vulcanizates provide elastomeric properties for automotive, medical, and other applications.
Preferred polyolefins, and their densities, are shown in Table I:
Random and block copolymers are recently developed copolymers in which particles of ethylene propylene rubber are distributed through a random copolymer polypropylene matrix. Random block copolymers display high stiffness and toughness, and the added softness of the random copolymer matrix results in less stress whitening than in impact copolymers. Random copolymers are produced by adding the comonomer, ethylene or, less commonly, 1-butene or 1-hexene, to the reactor during the polymerization reaction. The comonomer substitutes for propylene in the growing polymer chain. Insertions are randomly or statistically distributed along the chain and can consist of single monomers, or multiple monomers (two or more sequential ethylene molecules along the polymer chain). Random copolymers generally contain 1-7 wt. % ethylene, with 75% single and 25% multiple insertions. In practice, depending on the catalyst, polymerization conditions, and the reactivity of the comonomer compared to propylene, random copolymers can become somewhat blocky, with some regions of the polymer chain containing only polypropylene units and other regions containing only comonomer.
The structure of random copolymers is similar to isotactic polypropylene, but the regular, repeating arrangement of atoms is randomly disrupted by the presence of comonomer units. The effect is similar to that of increasing atacticity. Crystallinity is reduced, and mobility of the polymer chain is increased due to less stearic interaction of the pendant methyl groups of polypropylene.
Plastomers are very low density ( less than 0.880 g/cc) copolymers of ethylene and an olefin (such as ethylene-butene) produced using metallocene catalysts. Due to the single polymerization site on metallocene catalysts, comonomer can be inserted uniformly, producing a homogeneous copolymer with both elastomeric and plastic characteristics. They have a narrow molecular weight distribution and more long-chain branching.
Impact copolymers containing ethylene-propylene rubber are also useful as the matrix polymer and polymer intercalate in accordance with the present invention. Homopolymer formed in the first reactor is transferred to a second reactor, where copolymerization with ethylene is performed to produce ethylene-propylene rubber within the polypropylene matrix.
Other suitable polyolefins include poly(4-methyl(pentene-1), and elastomeric polyolefins, such as (1) poly(transisoprene); (2) poly(choloroprene); (3) poly(1,2 butadiene); (4) poly(styrene-co-butadiene); (5) nitrile rubber; (6) butyl rubber; (7) ethylene-propylene rubber (EPR); (8) ethylene-propylene-diene monomer rubber (EPDM), and the like.
Thermoplastic olefins (TPOs) are a blend of two polymer systems, with usually polypropylene or polyvinyl chloride as the crystalline matrix and ethylene propylene (EP) rubber, ethylene propylene diene monomer (EPDM), or metallocene-produced plastomers (i.e. ethylene-octene, ethylene-butene) as the elastomeric phase. The distinction between impact copolymers and thermoplastic olefins is not well defined; usually elastomer levels over about 20% are referred to as thermoplastic olefins. TPOs can be made by blending EPDM or EP rubber with polypropylene in a batch mixer or by forming the EP rubber phase during propylene polymerization in the reactor. Examples of other suitable blends are shown in Table II:
Depending on the formulation, thermoplastic olefins can be flexible or rigid; flexural moduli can range from 70 MPa (10,000 psi) to 2000 MPa (300,000 psi). Typical properties include high heat resistance, high melt flow, and superior low temperature impact resistance. Thermoplastic olefins can maintain ductile impact behavior at xe2x88x9234xc2x0 C. (xe2x88x9230xc2x0 F.).
In testing of equivalent 70/30 polypropylene/elastomer blends, plastomers doubled the weld-line strength and raised the melt index by up to 50% compared to EPDM, with a superior balance of flow and low-temperature impact properties. Plastomers maintained ductile behavior at xe2x88x9234xc2x0 C. (xe2x88x9230xc2x0 F.) with homopolymers of 4-35 g/10 minute melt flow indices, while EPDM and ethylene propylene monomer (EPM) blends were brittle with polypropylenes of 20 g/10 minute melt indices.
Thermoplastic vulcanizates (TPV), a type of thermoplastic elastomer, are a blend of a thermoplastic, usually polypropylene, and a rubber, similar to a thermoplastic olefin; however, the rubber phase in thermoplastic vulcanizates is crosslinked or vulcanized. EPDM is most commonly used as the elastomeric phase; other elastomers used include EP rubber, butyl rubber, and natural rubber. The elastomeric phase, consisting of small, 1-2 xcexcm rubber particles, is dispersed in the continuous polypropylene matrix. Elastomeric performance properties of the TPV are determined by the crosslinking of the elastomeric phase, while the polypropylene phase provides for melt processability. TPVs can be fully or partially crosslinked.
Other suitable polyolefin include poly(cycloolefin) homopolymers, such as cyclobutene, cyclopentene, and norbornene, and cycloolefin copolymers, such as those formed by co-polymerizing a cycloolefin homopolymer with ethylene, propylene, butylene or an xcex1-olefin to produce thermoplastic amorphous co-polymers.
The matrix polymer of the present invention may include various optional components which are additives commonly employed with polymeric compositions. Such optional components include nucleating agents, fillers, plasticizers, impact modifiers, chain extenders, plasticizers, colorants, mold release lubricants, antistatic agents, pigments, fire retardants, and the like. These optional components and appropriate amounts are well known to those skilled in the art.
The amount of intercalated layered material included may vary widely. It is preferred that the intercalate or platelet loading be less than about 10% by weight of the polymeric composition. Intercalate or platelet particle loadings within the range of about 0.01% to about 40% by weight, preferably about 0.05% to about 20%, more preferably about 0.5% to about 10% of the total weight of the composition.
In accordance with an important feature of the present invention, the intercalate and/or platelet/carrier compositions of the present invention can be manufactured in a concentrated form, e.g., as a concentrate, e.g., having about 10-90%, preferably about 20-80% intercalate and/or exfoliated platelets of layered material and about 10-90%, preferably about 20-80% matrix polymer. The concentrate can be dispersed in the matrix polymer and optionally exfoliated, before the addition of more matrix polymer to prevent degradation of the added matrix polymer by avoiding matrix polymerxe2x80x94degrading shearing.
When shear is employed for exfoliation, any method which can be used to apply a shear to the intercalate/matrix polymer nanocomposite composition can be used to exfoliate the platelets in the concentrate composition. The shearing action can be provided by any appropriate method, as for example by mechanical means, by thermal shock, by pressure alteration, or by ultrasonics, all known in the art. In particularly useful procedures, the concentrate composition is sheared by mechanical methods in which the intercalate concentrate, with or without the carrier or solvent, is sheared by use of mechanical means, such as stirrers, Banbury(copyright) type mixers, Brabender(copyright) type mixers, long continuous mixers, and extruders. Another procedure employs thermal shock in which shearing is achieved by alternatively raising or lowering the temperature of the concentrate composition causing thermal expansions and resulting in internal stresses which cause the shear. In still other procedures, shear is achieved by sudden pressure changes in pressure alteration methods; by ultrasonic techniques in which cavitation or resonant vibrations which cause portions of the concentrate composition to vibrate or to be excited at different phases and thus subjected to shear. These methods of shearing are merely representative of useful methods, and any method known in the art for shearing intercalates concentrate compositions may be used.
Mechanical shearing methods may be employed such as by extrusion, injection molding machines, Banbury(copyright) type mixers, Brabender(copyright) type mixers and the like. Shearing also can be achieved by introducing the layered material and co-intercalant oligomer(s) or polymer(s) at one end of an extruder (single or double screw) and receiving the sheared material at the other end of the extruder. The temperature of the layered material/intercalant oligomer or polymer composition, the length of the extruder, residence time of the composition in the extruder and the design of the extruder (single screw, twin screw, number of flights per unit length, channel depth, flight clearance, mixing zone, etc.) are several variables which control the amount of shear to be applied to the concentrate composition for exfoliation, prior to adding additional matrix oligomer or polymer.
In accordance with an important feature of the present invention, it has been found that the layered material can be intercalated with non-polar polymer co-intercalants by direct compounding, i.e., by mixing the layered material, e.g., smectite clay, directly with a non-polar polyolefin oligomer or polymer and, optionally a maleic anhydride-modified oligomer or polymer (together or separately) in an extruder to make the co-intercalated clay without significant exfoliation of the clay platelets. The resulting intercalate concentrate can be extruded into a homogeneous nanocomposite concentrate with unexpectedly homogenous dispersion of the intercalate, and after addition of a combination of a polyolefin matrix oligomer or polymer and a maleic anhydride-modified polyolefin matrix oligomer or polymer, the nanocomposite has exceptional strength characteristics. The intercalate concentrate dispersed within the matrix oligomers or matrix polymers is a combination of exfoliated individual platelets and multi-layer tactoids dispersed in the matrix polymers. The tactoids have the thickness of at least two individual platelet layers plus one to five monolayer thicknesses of co-intercalated polyolefin and maleic anhydride-modified polyolefin intercalants, and include small multiples or aggregates of platelets, in a coplanar aggregate, having oligomer or polymer co-intercalants bonded or complexed or ion-exchanged to the platelet surface(s).
Molding compositions comprising the combination of MA-PP and PP matrix oligomers or matrix polymers containing a desired loading of the intercalates of the present invention, and/or individual platelets obtained from exfoliation of the intercalates manufactured according to the present invention, are outstandingly suitable for the production of sheets, films and panels having valuable properties. Such sheets, films and panels may be shaped by conventional processes, such as vacuum processing or by hot pressing to form useful objects. The sheets and panels according to the invention are also suitable as coating materials for other materials comprising, for example, wood, glass, ceramic, metal or other plastics, and outstanding strengths can be achieved using conventional adhesion promoters, for example, those based on vinyl resins. The sheets, films and panels can be laminated to other plastic films, sheets or panels and this is preferably effected by co-extrusion, the sheets being bonded in the molten state. The surfaces of the sheets, films and panels, including those in the embossed form, can be improved or finished by conventional methods, for example by lacquering or by the application of protective films.
The nanocomposites of the present invention are also useful for fabrication of extruded films and film laminates, as for example, films for use in food packaging. Such films can be fabricated using conventional film extrusion techniques. The films are preferably from about 10 to about 100 microns, more preferably from about 20 to about 100 microns and most preferably from about 25 to about 75 microns in thickness.
The homogeneously distributed intercalate, and/or exfoliated platelets thereof, which has been intercalated in accordance with the present invention, to form an intercalate concentrate, is then combined with pristine (non-sheared) matrix oligomers or matrix polymers (e.g., MA-PP and PP) to form the preferred embodiment of the nanocomposite compositions of the present invention. The nanocomposite compositions can be formed into a film by suitable film-forming methods. Typically, the composition is melted and forced through a film forming die after oligomer or polymer intercalation and melt compounding. The film of the nanocomposite may go through sequential steps to cause the intercalate and/or exfoliated platelets thereof to be further oriented so the major planes through the intercalates and/or platelets thereof are substantially parallel to the major plane through the film. One method to accomplish this is to biaxially stretch the film. For example, the film is stretched in the axial or machine direction by tension rollers pulling the film as it is extruded from the die. The film is simultaneously stretched in the transverse direction by clamping the edges of the film and drawing them apart. Alternatively, the film is stretched in the transverse direction by using a tubular film die and blowing the film up as it passes from the tubular film die. The films may exhibit one or more of the following benefits in addition to decreased permeability to gases, particularly O2: increased modulus; increased wet strength; increased dimensional stability; and decreased moisture adsorption.
The nanocomposite intercalate composition may contain conventional additives such as UV stabilizers, flame, retardants, antioxidants, colorants, nucleating agents and plasticizers in conventional amounts.